Electrolyte Solution for Lithium Secondary Battery and Lithium Secondary Battery Including the Same

ABSTRACT

An electrolyte solution for a lithium secondary battery and a lithium secondary battery including the electrolyte solution are provided. The electrolyte solution includes an additive represented by Chemical Formula 1, an organic solvent and a lithium salt:wherein in Chemical Formula 1, R1 and R2 are each independently hydrogen or a substituted or unsubstituted C1-C5 alkyl group, X is O or S, and L is a substituted or unsubstituted C1-C5 alkylene group. The lithium secondary battery including the electrolyte solution provides enhanced high-temperature properties.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Applications No.10-2022-0082040 filed Jul. 4, 2022, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to an electrolyte solution and a lithiumsecondary battery comprising the same. More particularly, the presentdisclosure relates to an electrolyte solution comprising a solvent andan electrolytic salt, and a lithium secondary battery comprising thesame.

2. Description of Related Art

A secondary battery which can be charged and discharged repeatedly hasbeen widely employed as a power source of a mobile electronic devicesuch as a camcorder, a mobile phone, a laptop computer, etc.

A lithium secondary battery is actively developed and applied amongvarious types of secondary batteries due to high operational voltage andenergy density per unit weight, a high charging rate, a compactdimension, etc.

For example, the lithium secondary battery may include an electrodeassembly including a cathode, an anode and a separation layer, and anelectrolyte solution immersing the electrode assembly.

A lithium metal oxide may be used as an active material for a cathode ofthe lithium secondary battery. Examples of the lithium metal oxideinclude a nickel-based lithium metal oxide.

Surface damages of the nickel-based lithium metal oxide may occur due torepeated charge/discharge cycles to degrade power and capacity, and/or aside reaction may occur between the nickel-based lithium metal oxide andthe electrolyte, thereby reducing the service life of the lithiumsecondary battery.

As use of secondary batteries becomes more popular, the amount ofsecondary batteries being discarded as waste at the end of theirlifespan in increasing. Waste plastics, which are produced usingpetroleum as a feedstock, are difficult to recycle and are mostlydisposed of as garbage. These wastes take a long time to degrade innature, which causes contamination of the soil and serious environmentalpollution. For example, as plastic decomposes by exposure to sunlightand heat, the plastic waste releases greenhouse gases such as methaneand ethylene. Incineration of plastic waste releases significant amountsof greenhouse gases (GHG), such as carbon dioxide, nitrous oxide and/ormethane, into the environment. Carbon dioxide is the primary greenhousegas contributing to climate change. Therefore, it is desirable to reduceand/or prevent additional greenhouse gas emissions by increasing thelifespan of secondary batteries to reduce waste and/or ameliorate therelease of greenhouse gases into the environment by decomposition and/orincineration of the waste plastic associated with disposal of thesecondary batteries. By extending the lifespan of the secondarybatteries, environmental pollution and emission of greenhouse gases isreduced. Also, the plastic materials used in the secondary battery maybe recycled.

SUMMARY OF THE INVENTION

According to an aspect of the present disclosure, there is provided anelectrolyte solution providing improved high-temperature property.

According to an aspect of the present disclosure, there is provided alithium secondary battery having improved high-temperature property.

In some embodiments, there is provided an electrolyte solution for alithium secondary battery comprising an additive comprising a compoundrepresented by the following Chemical Formula 1; an organic solvent; anda lithium salt

wherein in Chemical Formula 1, R¹ and R² are each independently hydrogenor a substituted or unsubstituted C₁-C₅ alkyl group, X is O or S, and Lis a substituted or unsubstituted C₁-C₅ alkylene group.

In some embodiments, R¹ and R² may be each independently anunsubstituted C₁-C₃ alkyl group, X is O, and L is an unsubstituted C₁-C₃alkylene group.

In some embodiments, R¹ and R² may be each independently anunsubstituted C₁ alkyl group, X is O, and L is an unsubstituted C₁alkylene group.

In some embodiments, the additive may be comprised in an amount rangingfrom 0.1 wt % to 5 wt % based on a total weight of the electrolytesolution.

In some embodiments, the additive may be comprised in an amount rangingfrom 0.5 wt % to 2 wt % based on the total weight of the electrolytesolution.

In some embodiments, the organic solvent may comprise at least oneselected from the group consisting of a carbonate-based solvent, anester-based solvent, an ether-based solvent, a ketone-based solvent, analcohol-based solvent, an aprotic solvent, and mixtures thereof.

In some embodiments, the electrolyte solution may further comprise anauxiliary additive comprising at least one selected from the groupconsisting of a cyclic carbonate-based compound, a fluorine-substitutedcarbonate-based compound, a sultone-based compound, a cyclicsulfate-based compound, a phosphate-based compound, and mixturesthereof.

In some embodiments, the auxiliary additive may be comprised in anamount ranging from 0.05 wt % to 20 wt % based on a total weight of theelectrolyte solution.

In some embodiments, the auxiliary additive may be comprised in anamount ranging from 0.1 wt % to 15 wt % based on the total weight of theelectrolyte solution.

In some embodiments, there is provided a lithium secondary batterycomprising an electrode assembly in which a plurality of cathodes and aplurality of anodes are repeatedly stacked, a case accommodating theelectrode assembly, and the electrolyte solution for a lithium secondarybattery according to any of the embodiments disclosed hereinaccommodated together with the electrode assembly in the case.

In some embodiments, there is provided an electrolyte solutioncomprising an additive in an electrolyte solution for a lithiumsecondary battery that may form a robust solid electrolyte interphase(SEI) on an electrode surface.

Accordingly, a lithium secondary battery having improvedhigh-temperature storage properties (e.g., a capacity retention and/orprevention of resistance/thickness increase of the battery underhigh-temperature conditions) can be implemented.

The electrolyte solution for a lithium secondary battery as disclosedherein may provide a lithium secondary battery having improvedhigh-temperature stability (e.g., suppression of gas generation in ahigh-temperature environment).

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and characteristics of the present disclosure,as well as the functions of the related elements of structures and thecombination of components and economies of manufacture, will become moreapparent upon consideration of the disclosure herein with reference tothe accompanying drawings, all of which form a part of thisspecification, wherein like reference numerals designate correspondingparts in the various figures. It is to be expressly understood, however,that the drawings are for the purpose of illustration and descriptiononly and are not intended as a definition of the limit of the invention.

Further features and other examples and advantages will become apparentfrom the following detailed description made with reference to thedrawings in which:

FIG. 1 is a schematic plan view illustrating a lithium secondary batteryin accordance with example embodiments.

FIG. 2 is a schematic cross-sectional view illustrating a lithiumsecondary battery in accordance with example embodiments.

FIG. 3 is a graph showing capacity retentions of secondary batteriesaccording to Example and Comparative Example under a high temperature(60° C.) condition.

FIG. 4 is a graph showing resistance increase ratios of secondarybatteries according to Example and Comparative Example under a hightemperature (60° C.) condition.

FIG. 5 is a graph showing thickness increase ratios of secondarybatteries according to Example and Comparative Example under a hightemperature (60° C.) condition.

DESCRIPTION OF THE INVENTION

According to embodiments of the present invention, there is provided anelectrolyte solution which comprises an additive having a predeterminedchemical structure disclosed herein. Also, there is provided a lithiumsecondary battery comprising the electrolyte solution.

Throughout the specification, unless explicitly described to thecontrary, “comprising”, “including” or “containing” any constituentelements will be understood to imply further inclusion of otherconstituent elements.

Unless the context clearly indicates otherwise, the singular forms ofthe terms used in the present specification may be interpreted asincluding the plural forms. As used herein, the singular form of “a”,“an”, and “the” include plural referents unless the context clearlystates otherwise.

For the purposes of this specification, unless otherwise indicated, allnumbers expressing quantities of ingredients, reaction conditions,dimensions, physical characteristics, and so forth used in thespecification and claims are to be understood as being modified in allinstances by the term “about.” Hereinafter, unless otherwise definedherein, “about” may be considered as a value within 30%, 25%, 20%, 15%,10%, 5%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05% or 0.01 of the specified value.Unless indicated to the contrary, the numerical parameters set forth inthe following specification and attached claims are approximations thatcan vary depending upon the desired properties sought to be obtained bythe present invention.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include any and all sub-ranges betweenand including the recited minimum value of 1 and the recited maximumvalue of 10, that is, all subranges beginning with a minimum value equalto or greater than 1 and ending with a maximum value equal to or lessthan 10, and all subranges in between, e.g., 1 to 6.3, or 5.5 to 10, or2.7 to 6.1.

In the present specification, the term “A-based compound” may refer to acompound comprising a group A and/or a derivative of the compound.

In the present specification, the term “Ca-Cb” refers that the number ofcarbon (C) atoms is from a to b.

Electrolyte Solution for Lithium Secondary Battery

In some embodiments, there is provided an electrolyte solution for alithium secondary battery comprising a lithium salt, organic solventsand an additive comprising a compound represented by Chemical Formula 1.

Hereinafter, components of the electrolyte solution for a lithiumsecondary battery will be described in detail.

Additive

The electrolyte solution for a lithium secondary battery according tosome embodiments may comprise an additive comprising a compoundrepresented by Chemical Formula 1

wherein in Chemical Formula 1, R¹ and R² are each independently hydrogenor a substituted or unsubstituted C₁-C₅ alkyl group, X is O or S, and Lis a substituted or unsubstituted C₁-C₅ alkylene group.

In some embodiments, R¹ and R² may be chemically the same as ordifferent from each other.

For example, R¹ may be hydrogen or a substituted or unsubstituted C₁-C₅alkyl group, or R¹ may be an unsubstituted C₁-C₃ alkyl group, or R¹ maybe an unsubstituted C₁ alkyl group (a methyl group).

For example, R² may be hydrogen or a substituted or unsubstituted C₁-C₅alkyl group, or R² may be an unsubstituted C₁-C₃ alkyl group, e.g., anunsubstituted C₁ alkyl group (a methyl group).

For example, X may be O or S. O represents oxygen and S representssulfur. In some embodiments, X may be O.

For example, L may be a substituted or unsubstituted C₁-C₅ alkylenegroup, or L may be a substituted or unsubstituted C₁-C₃ alkylene group,e.g., an unsubstituted C₁ alkylene group (a methylene group).

For example, the alkyl group may mean a portion in a molecule composedof carbon and hydrogen. The alkyl group may mean a partial remainingstructure assuming that one hydrogen atom is removed from the alkane(C_(n)H_(2n+2)). For example, CH₃—CH₂—CH₂— indicates a propyl group.

For example, the alkylene group may refer to a structure in which onehydrogen atom is separated from each of carbon atoms at both terminalsof an alkane. For example, —CH₂—CH₂—CH₂— indicates a propylene group.

For example, the term “substituted” used herein refers that asubstituent may be further bonded to a carbon atom of the alkyl group orthe alkylene group by substituting a hydrogen atom of the alkyl group orthe alkylene group with the substituent. For example, the substituentmay be at least one of a halogen, a C₁-C₆ alkyl group, a C₂-C₆ alkenylgroup, an amino group, a C₁-C₆ alkoxy group, a C₃-C₇ cycloalkyl group,or a 5 to 7-membered hetero-cycloalkyl group. In some embodiments, thesubstituent may be a halogen or a C₁-C₆ alkyl group.

The additive comprising the compound represented by Chemical Formula 1may be comprised in the electrolyte solution for a secondary battery, sothat a robust solid electrolyte interphase (SEI) layer may be formed onan electrode through a decomposition reaction of a cyclic ether.

For example, the solid electrolyte interphase layer based on a sulfonatefunctional group may be formed under a high temperature condition. Insome embodiments, the solid electrolyte interphase layer may be formedon an anode. Accordingly, decomposition of an organic solvent (e.g., EC,EMC, etc.) may be effectively prevented, and gas generation and batterythickness increase may be significantly reduced.

In some embodiments, the compound represented by Chemical Formula 1 maycomprise 3-(mesyloxymethyl)-3-methyloxetane. For example, the3-(mesyloxymethyl)-3-methyloxetane may be represented by ChemicalFormula 1-1:

3-(mesyloxymethyl)-3-methyloxetane may be comprised as the additive ofthe electrolyte solution for a secondary battery, so that a stable SEIlayer may be formed on the anode by the sulfonate group. Accordingly, alithium secondary battery having improved high-temperature storageproperties may be implemented. Additionally, decomposition of theelectrolyte due to a reaction between the electrolyte solution and theanode may be suppressed to suppress gas generation.

In some embodiments, a content of the additive content may be adjustedto be 0.1 weight percent (wt %) or more, 0.2 wt % or more, 0.3 wt % ormore, 0.4 wt % or more, 0.5 wt % or more, or 1 wt % or more based on atotal weight of the electrolyte solution in consideration of sufficientpassivation and stable SEI film formation.

In some embodiments, the content of the additive may be adjusted to be10 wt % or less, 9 wt % or less, 7 wt % or less, 6 wt % or less, 5 wt %or less, 4.5 wt % or less, 4 wt % or less, 3.5 wt % or less, 3 wt % orless, or 2 wt % or less based on the total weight of the electrolytesolution in consideration of lithium ion mobility and active materialactivity in the electrolyte solution.

In some embodiments, the content of the additive may be in a range from0.1 wt % to 5 wt %, or from 0.5 wt % to 2 wt %. Within the above range,the above-described anode passivation may be sufficiently implementedwhile preventing an excessive degradation of lithium ion mobility andactivity of a cathode active material. Further, increase of a batteryresistance and a battery thickness may be prevented under hightemperature conditions.

Auxiliary Additive

The electrolyte solution for a rechargeable lithium battery may furthercomprise an auxiliary additive together with the above-describedadditive.

The auxiliary additive may comprise, e.g., a cyclic carbonate-basedcompound, a fluorine-substituted carbonate-based compound, asultone-based compound, a cyclic sulfate-based compound and/or aphosphate-based compound.

In some embodiments, a content of the auxiliary additive may be adjustedto be 10 wt % or less, 9 wt % or less, 8 wt % or less, 7 wt % or less, 6wt % or less, 5wt % or less, 4 wt % or less, 3 wt % or less, 2 wt % orless, or 1 wt % or less based on the total weight of the electrolytesolution in consideration of an interaction with the additive comprisingthe compound represented by Chemical Formula 1

In some embodiments, the content of the auxiliary additive may beadjusted to be 0.01 wt % or more, 0.02 wt % or more, 0.03 wt % or more,0.05 wt % or more, 0.1 wt % or more, 0.2 wt % or more, 0.3 wt % or more,0.4 wt % or more, or 0.5 wt % or more in consideration of the SEI filmstabilization.

In some embodiments, the auxiliary additive may be comprised in anamount from 0.05 wt % to 20 wt %, from 0.1 wt % to 15 wt %, or from 0.1wt % to 10 wt % based on the total weight of the electrolyte solution.Within the above range, durability of the protective film may beenhanced and high-temperature storage properties may be improved withoutdegrading the function of the main additive.

The cyclic carbonate-based compound may comprise vinylene carbonate(VC), and/or vinyl ethylene carbonate (VEC), etc.

The fluorine-substituted cyclic carbonate-based compound may comprisefluoroethylene carbonate (FEC).

The sultone-based compound may comprise 1,3-propane sultone, 1,3-propenesultone, and/or 1,4-butane sultone. etc.

The cyclic sulfate-based compound may comprise 1,2-ethylene sulfate,and/or 1,2-propylene sulfate, etc.

The phosphate-based compound may comprise an oxalatophosphate-basedcompound such as lithium bis(oxalato)phosphate.

In some embodiments, the fluorine-substituted cyclic carbonate-basedcompound, the sultone-based compound, the cyclic sulfate-based compoundand the oxalatophosphate-based compound may be used together as theauxiliary additive.

Durability and stability of the electrode may be further improved by theaddition of the auxiliary additive. The auxiliary additive may becomprised in an appropriate amount within a range that does not inhibitthe lithium ion mobility in the electrolyte solution.

Organic Solvent and Lithium Salt

The organic solvent may comprise an organic compound that providessufficient solubility for the lithium salt, the additive and theauxiliary additive and may have no substantial reactivity in thebattery.

For example, the organic solvent may comprise a carbonate-based solvent,an ester-based solvent, an ether-based solvent, a ketone-based solvent,an alcohol-based solvent, and/or an aprotic solvent, etc. These may beused alone or in a combination thereof.

In some embodiments, the organic solvent may comprise a carbonate-basedsolvent. The carbonate-based solvent may comprise a linearcarbonate-based solvent and/or a cyclic carbonate-based solvent.

For example, the linear carbonate-based solvent may comprise at leastone of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethylcarbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate and/ordipropyl carbonate.

For example, the cyclic carbonate-based solvent may comprise at leastone of ethylene carbonate (EC), propylene carbonate (PC) and/or butylenecarbonate.

In some embodiments, in the organic solvent, an amount of the linearcarbonate-based solvent may be greater than an amount of the cycliccarbonate-based solvent on a volume basis.

For example, a mixed volume ratio of the linear carbonate-based solventand the cyclic carbonate-based solvent may be from 1:1 to 9:1, or from1.5:1 to 4:1 in some embodiments.

For example, the ester-based solvent may comprise at least one of methylacetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA),1,1-dimethylethyl acetate (DMEA), methyl propionate (MP) and/or ethylpropionate (EP).

For example, the ether-based solvent may comprise at least one ofdibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethyleneglycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF)and/or 2-methyltetrahydrofuran.

For example, the ketone-based solvent may comprise cyclohexanone. Thealcohol-based solvent may comprise, e.g., at least one of ethyl alcoholand/or isopropyl alcohol.

For example, the aprotic solvent may comprise at least one of anitrile-based solvent, an amide-based solvent (e.g., dimethylformamide),a dioxolane-based solvent (e.g., 1,3-dioxolane), and/or asulfolane-based solvent, etc. These may be used alone or in acombination thereof.

The electrolyte may comprise, e.g., a lithium salt. For example, thelithium salt may be expressed as Li⁺X⁻. Non-limiting examples of theanion X⁻ may comprise F⁻, Cl⁻, Br⁻, I⁻, NO₃ ⁻, N(CN)₂ ⁻, BF₄ ⁻, ClO₄ ⁻,PF₆ ⁻, (CF₃)₂PF₄ ⁻, (CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻, (CF₃)₆P⁻,CF₃SO₃ ⁻, CF₃CF₂SO₃ ⁻, (CF₃SO₂)₂N⁻, (FSO₂)₂N⁻, CF₃CF₂(CF₃)₂CO⁻,(CF₃SO₂)₂CH⁻, (SF₅)₃C⁻, (CF₃SO₂)₃C⁻, CF₃(CF₂)₇SO₃ ⁻, CF₃CO₂ ⁻, CH₃CO₂ ⁻,SCN⁻, or (CF₃CF₂SO₂)₂N⁻, etc.

In some embodiments, the lithium salt may comprise at least one of LiBF₄and/or LiPF₆.

In an embodiment, the lithium salt may be comprised in a concentrationfrom 0.01 M to 5M, or from 0.01 M to 2M with respect to the organicsolvent. Within the above range, transfer of lithium ions and/orelectrons may be promoted during charging and discharging of the lithiumsecondary battery.

Lithium Secondary Battery

According to some embodiments, a lithium secondary battery havingimproved high-temperature stability and storage property is providedusing the electrolyte solution.

FIGS. 1 and 2 are a schematic plan view and a schematic cross-sectionalview, respectively, illustrating a lithium secondary battery inaccordance with exemplary embodiments. FIG. 2 is cross-sectional viewtaken along a line I-I′ of FIG. 1 .

Referring to FIGS. 1 and 2 , a lithium secondary battery may comprise anelectrode assembly comprising a cathode 100 and an anode 130 facing thecathode 100.

The cathode 100 may comprise a cathode current collector 105 and acathode active material layer 110 on the cathode current collector 105.The cathode active material layer 110 may comprise a cathode activematerial. The cathode active material layer 110 may further comprise acathode binder and a conductive material.

For example, a cathode slurry may be prepared by mixing and stirring thecathode active material, the cathode binder, the conductive material, adispersive medium, etc., and then the cathode slurry may be coated onthe cathode current collector 105, dried and pressed to form the cathode100.

For example, the cathode current collector 105 may comprise stainlesssteel, nickel, aluminum, titanium, copper, and/or an alloy thereof.

The cathode active material may comprise lithium metal oxide particlescapable of reversibly intercalating and de-intercalating lithium ions.In an embodiment, the cathode active material may comprise lithium metaloxide particles containing nickel.

In some embodiments, the lithium metal oxide particle may comprise 80mol % or more of nickel based on a total number of moles of all elementsexcept lithium and oxygen. In this case, the lithium secondary batteryhaving a high capacity may be implemented.

In some embodiments, the lithium metal oxide particle may comprise 83mol % or more, 85 mol % or more, 90 mol % or more, or 95 mol % or moreof nickel based on the total number of moles of all elements exceptlithium and oxygen.

In some embodiments, the lithium metal oxide particle may furthercomprise at least one of cobalt and/or manganese.

In some embodiments, the lithium metal oxide particle may furthercomprise cobalt and manganese. In this case, the lithium secondarybattery having enhanced power and penetration stability may beimplemented.

In some embodiments, the lithium metal oxide particle may be representedby Chemical Formula 2 below.

Li_(x)Ni_((1−a−b))Co_(a)M_(b)O_(y)  [Chemical Formula 2]

In some embodiments, in Chemical Formula 2, M may comprise at least oneof Al, Zr, Ti, Cr, B, Mg, Mn, Ba, Si, Y, W and/or Sr, 0.9≤x≤1.2,1.9≤y≤2.1, and 0≤a+b≤0.5.

In some embodiments, 0a<+b≤0.4, 0<a+b≤0.3, 0<a+b≤0.2, 0<a+b≤0.17,0<a+b≤0.15, 0<a+b≤0.12, and 0<a+b≤0.1.

In some embodiments, the lithium metal oxide particles may furthercomprise a coating element or a doping element. In some embodiments, thecoating element or doping element may comprise Al, Ti, Ba, Zr, Si, B,Mg, P, Sr, W, La, an alloy thereof, and/or an oxide thereof. In thiscase, the lithium secondary battery having improved life-span propertiesmay be implemented.

In some embodiments, the cathode binder may comprise an organic basedbinder such as polyvinylidenefluoride (PVDF), a polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile,and/or polymethylmethacrylate, etc., or an aqueous based binder such asstyrene-butadiene rubber (SBR) that may be used with a thickener such ascarboxymethyl cellulose (CMC).

In some embodiments, the conductive material may comprise a carbon-basedmaterial such as graphite, carbon black, graphene, and/or carbonnanotube, etc., a metal-based material such as tin, tin oxide, titaniumoxide, and/or a perovskite material such as LaSrCoO₃ and/or LaSrMnO₃,etc.

In some embodiments, the anode 130 may comprise an anode currentcollector 125 and an anode active material layer 120 on the anodecurrent collector 125. The anode active material layer 120 may comprisean anode active material, and may further comprise an anode binder and aconductive material.

In some embodiments, the anode active material may be mixed and stirredtogether with a binder and conductive material, etc., in a solvent toform an anode slurry. The anode slurry may be coated on the anodecurrent collector 125, dried and pressed to obtain the anode 130.

In some embodiments, the anode current collector 125 may comprise gold,stainless steel, nickel, aluminum, titanium, copper, and/or an alloythereof. In some embodiments, the anode current collector 125 maycomprise copper or a copper alloy.

In some embodiments, the anode active material may be a material capableof intercalating and de-intercalating lithium ions. For example, theanode active material may comprise a lithium alloy, a carbon-basedmaterial, and/or a silicon-based material, etc.

In some embodiments, the lithium alloy may comprise a metal element suchas aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin,gallium, and/or indium, etc.

In some embodiments, the carbon-based material may comprise acrystalline carbon, an amorphous carbon, a carbon composite, and/or acarbon fiber, etc.

In some embodiments, the amorphous carbon may comprise hard carbon,coke, a mesocarbon microbead (MCMB) calcined at 1500° C. or less, and/ora mesophase pitch-based carbon fiber (MPCF), etc. In some embodiments,the crystalline carbon may comprise, e.g., natural graphite, graphitizedcoke, graphitized MCMB, and/or graphitized MPCF, etc.

In some embodiments, the anode active material may comprise thesilicon-based material. For example, the silicon-based material maycomprise Si, SiOx (0<x<2), Si/C, SiO/C, and/or a Si-Metal, etc. In thiscase, a lithium secondary battery having a high capacity may beimplemented.

For example, when the anode active material comprises the silicon-basedmaterial, the battery thickness may be increased during repeatedcharging and discharging. The lithium secondary battery according toembodiments of the present disclosure may comprise the above-describedelectrolyte solution, so that the increase of the battery thickness maybe reduced or suppressed.

In some embodiments, a content of the silicon-based active material inthe anode active material may be in a range from 1 wt % to 20 wt %, 1 wt% to 15 wt %, or 1 wt % to 10 wt %.

In some embodiments, the anode binder and the conductive material maycomprise materials substantially the same as or similar theabove-described cathode binder and conductive material. In someembodiments, the anode binder may comprise the aqueous binder such asstyrene-butadiene rubber (SBR) that may be used together with athickener such as carboxymethyl cellulose (CMC).

In some embodiments, a separation layer 140 may be interposed betweenthe cathode 100 and the anode 130.

In some embodiments, an area of the anode 130 may be greater than anarea of the cathode 100. In this case, lithium ions generated from thecathode 100 may be easily transferred to the anode 130 without beingprecipitated.

In some embodiments, the separation layer 140 may comprise a porouspolymer film prepared from, e.g., a polyolefin-based polymer such as anethylene homopolymer, a propylene homopolymer, an ethylene/butenecopolymer, an ethylene/hexene copolymer, an ethylene/methacrylatecopolymer, and/or the like. In some embodiments, the separation layer140 may also comprise a non-woven fabric formed from a glass fiber witha high melting point, a polyethylene terephthalate fiber, and/or thelike.

In some embodiments, an electrode cell may be defined by the cathode100, the anode 130 and the separation layer 140, and a plurality of theelectrode cells may be stacked to form an electrode assembly 150. Insome embodiments, the electrode assembly 150 may be formed by winding,laminating or z-folding of the separation layer 140.

The lithium secondary battery according to some embodiments may comprisea cathode lead 107 connected to the cathode 100 to protrude to anoutside of a case 160, and an anode lead 127 connected to the anode 130to protrude to the outside of the case 160.

In some embodiments, the cathode lead 107 may be electrically connectedto the cathode current collector 105. The anode lead 127 may beelectrically connected to the anode current collector 125.

In some embodiments, the cathode current collector 105 may comprise aprotrusion (a cathode tab, not illustrated) at one side thereof. Thecathode active material layer 110 may not be formed on the cathode tab.The cathode tab 106 may be integral with the cathode current collector105 or may be connected to the cathode current collector 105 by, e.g.,welding. The cathode current collector 105 and the cathode lead 107 maybe electrically connected via the cathode tab.

In some embodiments, the anode current collector 125 may comprise aprotrusion (an anode tab, not illustrated) at one side thereof. Theanode active material layer 120 may not be formed on the anode tab. Theanode tab 126 may be integral with the anode current collector 125 ormay be connected to the anode current collector 125 by, e.g., welding.The anode electrode current collector 125 and the anode lead 127 may beelectrically connected via the anode tab.

In some embodiments, the electrode assembly 150 may comprise a pluralityof the cathodes and a plurality of the anodes. In some embodiments, thecathodes and the anodes may be alternately disposed, and the separationlayer may be interposed between the cathode and the anode. Each of theplurality of the cathodes may comprise the cathode tab. Each of theplurality of the anodes may comprise the anode tab.

In some embodiments, the cathode tabs (or the anode tabs) may belaminated, pressed and welded to form a cathode tab stack (or an anodetab stack). The cathode tab stack may be electrically connected to thecathode lead 107. The anode tab stack may be electrically connected tothe anode lead 127.

In some embodiments, the electrode assembly 150 may be accommodatedtogether with the electrolyte solution according to the above-describedembodiments in a case 160 to form the lithium secondary battery.

In some embodiments, the lithium secondary battery may be fabricatedinto a cylindrical shape using a can, a prismatic shape, a pouch shape,a coin shape, etc.

A method is provided for reducing greenhouse gas emissions, comprising:preparing a lithium secondary battery, comprising: an electrode assemblyin which a plurality of cathodes and a plurality of anodes arerepeatedly stacked; a case accommodating the electrode assembly; and anelectrolyte solution for a lithium secondary battery, comprising: anadditive comprising a compound represented by Chemical Formula 1; anorganic solvent; and a lithium salt:

wherein, in Chemical Formula 1, R¹ and R² are each independentlyhydrogen or a substituted or unsubstituted C₁-C₅ alkyl group, X is O orS, and L is a substituted or unsubstituted C₁-C₅ alkylene group,accommodated together with the electrode assembly in the case.

A method is provided for reducing environmental pollution from a lithiumsecondary battery, comprising: preparing a lithium secondary battery,comprising: an electrode assembly in which a plurality of cathodes and aplurality of anodes are repeatedly stacked; a case accommodating theelectrode assembly; and an electrolyte solution for a lithium secondarybattery, comprising: an additive comprising a compound represented byChemical Formula 1; an organic solvent; and a lithium salt:

wherein, in Chemical Formula 1, R¹ and R² are each independentlyhydrogen or a substituted or unsubstituted C₁-C₅ alkyl group, X is O orS, and L is a substituted or unsubstituted C₁-C₅ alkylene group,accommodated together with the electrode assembly in the case.

In some embodiments, the lithium secondary batteries or portions thereofmay be recycled.

Hereinafter, specific examples and comparative examples are proposed tomore concretely describe the present invention. However, the followingexamples are only given for illustrating the present invention and thoseskilled in the related art will obviously understand that variousalterations and modifications are possible within the scope and spiritof the present invention.

Examples and Comparative Examples

(1) Synthesis Example of Additive (3-(mesyloxymethyl)-3-methyloxetane)

3-methyl-3-oxetanemethanol (2.14 g, 21.0 mmol), triethylamine (4.4 ml,31.5 mmol) and 100 ml of dichloromethane were sequentially added to around-bottom flask to prepare a reaction solution, and then stirred.After cooling to 0° C., methanesulfonyl chloride (2.64 g, 23.1 mmol)diluted with 10 ml of dichloromethane was slowly added to the reactionsolution. Thereafter, the mixture was reacted while being stirred for 2hours and maintaining the temperature.

The obtained product was washed with distilled water and saturatedsodium chloride aqueous solution. The solvent was removed from theorganic layer under reduced pressure and purified by a silica gel columnchromatography to obtain 3.6 g of 3-(mesyloxymethyl)-3-methyloxetane asa yellow liquid sample (yield: 95%).

¹H-NMR (500 MHz, CDCl₃): 4.52 (2H, d), 4.43 (2H, d), 4.32 (2H, s), 3.07(3H, s), 1.40 (3H, s)

(2) Preparation of Electrolyte Solution

A 1.0 M LiPF₆ solution (EC/EMC/DEC mixed solvent in a 25:45:30 volumeratio) was prepared.

In the LiPF₆ solution, the additive and auxiliary additives were addedand mixed with contents (wt %) shown in Table 1 below based on a totalweight of an electrolyte solution to form electrolyte solutions ofExamples and Comparative Examples.

(5) Fabrication of Lithium Secondary Battery Sample

Li[Ni_(0.8)Co_(0.1) Mn_(0.1)]O₂, carbon black and polyvinylidenefluoride (PVDF) were dispersed in N-methyl pyrrolidone (NMP) in a weightratio of 98:1:1 to prepare a cathode slurry.

The cathode slurry was uniformly coated on a region of an aluminum foilhaving a protrusion (cathode tab) except for the protrusion, and driedand pressed to prepare a cathode.

Anode active material comprising graphite and SiOx (0<x<2) in a weightratio of 91:6, styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC) were dispersed in water by a weight ratio of 97:0.1:2.9to form an anode slurry.

The anode slurry was uniformly coated on a region of a copper foilhaving a protrusion (anode tab) except for the protrusion, and dried andpressed to prepare an anode.

An electrode assembly was formed by interposing a polyethylene separatorbetween the cathode and the anode. A cathode lead and an anode lead wereconnected to the cathode tab and the anode tab, respectively, bywelding.

The electrode assembly was accommodated in a pouch (case) so thatpartial regions of the cathode lead and the anode lead were exposed toan outside, and three sides except for an electrolyte injection sidewere sealed.

A lithium secondary battery sample was prepared by injecting theelectrolyte solution prepared in the above (1), sealing the electrolyteinjection side, and then impregnating for 12 hours.

TABLE 1 auxiliary additive (wt %) additive LiPO₂F₂ FEC PS ESA Example 1additive I, 0.5 wt % 1 3 0.5 0.5 Comparative — 1 3 0.5 0.5 Example 1Comparative additive II, 0.5 wt % 1 3 0.5 0.5 Example 2

-   -   The components listed in Table 1 are as follows.    -   Additive I: 3 -(Mesyloxymethyl)-3 -methyloxetane    -   Additive II: oxiran-2-ylmethyl methanesulfonate    -   LiPO₂F₂: lithium difluorophosphate    -   FEC: fluoro ethylene carbonate    -   PS: 1,3-propane sultone    -   ESA: ethylene sulfate

Experimental Example (1) Measurement of Capacity Retention (Ret) AfterHigh Temperature Storage

The lithium secondary batteries of Examples and Comparative Exampleswere subjected to 0.5 C CC/CV charging (4.2V, 0.05 C CUT-OFF) and 0.5 CCC discharging (2.7V CUT-OFF) at 25° C. by three cycles, and a dischargecapacity C1 at the 3rd cycle was measured.

After storing the charged lithium secondary battery at 60° C. for 16weeks, the batteries were additionally maintained at room temperaturefor 30 minutes, and a discharge capacity C2 was measured by 0.5 C CCdischarging (2.75V CUT-OFF). A capacity retention was calculated asfollows. The results are shown in Table 2 below and FIG. 3 .

Capacity Retention (%)=C2/C1×100 (%)

(2) Measurement of Internal Resistance (DCIR) Increase Ratio After HighTemperature Storage

The lithium secondary battery of each Examples and Comparative Exampleswas 0.5 C CC/CV charged (4.2V 0.05 C CUT-OFF) at 25° C., and then 0.5 CCC discharged until a SOC 60%. At the SOC 60% point, DCIR R1 wasmeasured by discharging for 10 seconds and complementary charging whilechanging the C-rate to 0.2 C, 0.5 C, 1 C, 1.5 C, 2 C and 2.5 C

The charged lithium secondary battery was exposed to air at 60° C. for16 weeks. The battery was further left at room temperature for 30minutes, and then DCIR R2 was measured by the same method as describedabove. An internal resistance increase ratio was calculated as follows.The results are shown in Table 2 below and FIG. 4 .

Internal resistance increase ratio (%)=(R2−R1)/R1×100 (%)

(3) Measurement of Battery Thickness After High Temperature Storage

After charging the lithium secondary batteries of Examples andComparative Examples at 25° C. under conditions of 0.5 C CC/CV (4.2V0.05 C CUT-OFF), a battery thickness T1 was measured.

After exposing the charged lithium secondary batteries to air at 60° C.for 16 weeks (using a thermostat), a battery thickness T2 was measured.The battery thickness was measured using a plate thickness measuringdevice (Mitutoyo, 543-490B). A battery thickness increase ratio wascalculated as follows. The results are shown in Table 2 below and FIG. 5.

Battery thickness increase ratio (%)=(T2−T1)/T1×100 (%)

TABLE 2 high temperature storage properties DCIR increase thicknessincrease Ret.(%) ratio (%) ratio (%) Example 1 73.6 155.7 125.7Comparative 73.2 169.6 136.9 Example 1 Comparative 73.0 163.0 128.5Example 2

Referring to Table 2 and FIGS. 3 to 5 , the high-temperature storageperformance of the lithium secondary battery of Example 1 was improved.

Specifically, in the lithium secondary battery of Example 1, theresistance increase was suppressed, and gas generation was suppressedthereby reducing the thickness increase ratio.

Additionally, the lithium secondary battery of Example 1 using acompound having a tetrahedral ring ether and a sulfonate group as theadditive provided improved high temperature storage properties comparedto those from the lithium secondary battery of Comparative Example 2using a compound having a tricyclic ether and a sulfonate group as theadditive.

What is claimed is:
 1. An electrolyte solution for a lithium secondarybattery, comprising: an additive comprising a compound represented byChemical Formula 1; an organic solvent; and a lithium salt:

wherein, in Chemical Formula 1, R¹ and R² are each independentlyhydrogen or a substituted or unsubstituted C₁-C₅ alkyl group, X is O orS, and L is a substituted or unsubstituted C₁-C₅ alkylene group.
 2. Theelectrolyte solution for a lithium secondary battery of claim 1, whereinR¹ and R₂ are each independently an unsubstituted C₁-C₃ alkyl group, Xis O, and L is an unsubstituted C₁-C₃ alkylene group.
 3. The electrolytesolution for a lithium secondary battery of claim 1, wherein R¹ and R²are each independently an unsubstituted C₁ alkyl group, X is O, and L isan unsubstituted C₁ alkylene group.
 4. The electrolyte solution for alithium secondary battery of claim 1, wherein the additive is comprisedin an amount ranging from 0.1 wt % to 5 wt % based on a total weight ofthe electrolyte solution.
 5. The electrolyte solution for a lithiumsecondary battery of claim 1, wherein the additive is comprised in anamount ranging from 0.5 wt % to 2 wt % based on the total weight of theelectrolyte solution.
 6. The electrolyte solution for a lithiumsecondary battery of claim 1, wherein the organic solvent comprises atleast one selected from the group consisting of a carbonate-basedsolvent, an ester-based solvent, an ether-based solvent, a ketone-basedsolvent, an alcohol-based solvent, an aprotic solvent, and mixturesthereof.
 7. The electrolyte solution for a lithium secondary battery ofclaim 1, wherein the electrolyte solution further comprises an auxiliaryadditive comprising at least one selected from the group consisting of acyclic carbonate-based compound, a fluorine-substituted carbonate-basedcompound, a sultone-based compound, a cyclic sulfate-based compound, aphosphate-based compound, and mixtures thereof.
 8. The electrolytesolution for a lithium secondary battery of claim 7, wherein theauxiliary additive is comprised in an amount ranging from 0.05 wt % to20 wt % based on a total weight of the electrolyte solution.
 9. Theelectrolyte solution for a lithium secondary battery of claim 7, whereinthe auxiliary additive is comprised in an amount ranging from 0.1 wt %to 15 wt % based on the total weight of the electrolyte solution.
 10. Alithium secondary battery, comprising: an electrode assembly in which aplurality of cathodes and a plurality of anodes are repeatedly stacked;a case accommodating the electrode assembly; and the electrolytesolution for a lithium secondary battery of claim 1 accommodatedtogether with the electrode assembly in the case.
 11. A method forreducing greenhouse gas emissions, comprising: preparing a lithiumsecondary battery, comprising: an electrode assembly in which aplurality of cathodes and a plurality of anodes are repeatedly stacked;a case accommodating the electrode assembly; and an electrolyte solutionfor a lithium secondary battery, comprising: an additive comprising acompound represented by Chemical Formula 1; an organic solvent; and alithium salt:

wherein, in Chemical Formula 1, R¹ and R² are each independentlyhydrogen or a substituted or unsubstituted C₁-C₅ alkyl group, X is O orS, and L is a substituted or unsubstituted C₁-C₅ alkylene group,accommodated together with the electrode assembly in the case.